【正文】 最初的數(shù)控系統(tǒng)下今天應(yīng)用的數(shù)控系統(tǒng)是有很大差別的。數(shù)控這個概念是50年代初在美國空軍的資助下提出來的。一個數(shù)控技師的工作不是去操縱機床，而是編寫能夠發(fā)出機床操縱指令的程序。然而，操作工人的大部分時間卻花費在簡單的重復(fù)調(diào)整和觀察切屑過程上。普通車床是生產(chǎn)中最經(jīng)常使用的車床種類。它是一個直徑通常大約在51~76mm（2~3英寸）之間的鋼制空心圓柱體。由于機床的精度在很大程度上取決于主軸，因此，主軸的結(jié)構(gòu)尺寸較大，通常安裝在預(yù)緊后的重型圓錐滾子軸承或球軸承中。導(dǎo)軌上的任何誤差，常常意味著整個機床的精度遭到破壞。車床的基本部件有：床身、主軸箱組件、尾座組件、溜板組件、絲杠和光杠。 singlespindle automatics, multiplespindle automatics and automatic chucking machines. Originally designed for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has long since exceeded Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a reader.Numerical control was developed to overe the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can produce parts more uniformly, they are faster, and the longrun tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology: Electrical discharge machining,Laser cutting,Electron beam welding.Numerical control has also made machine tools more versatile than their manually operated predecessors. An NC machine tool can automatically produce a wide of parts, each involving an assortment of widely varied and plex machining processes. Numerical control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tolls and processes.Like so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the . Air Force. In its earliest stages, NC machines were able to made straight cuts efficiently and effectively. However, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter the straight lines making up the steps, the smoother is the curve, Each line segment in the steps had to be calculated. This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major step forward in the fur ther development from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development.A major problem was the fragility of the punched paper tape medium. It was mon for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacer